A spatial light modulator (SLM) is a transducer that modulates incident light in a spatial pattern that corresponds to an optical or electrical input. A type of SLM is the SLM based on microelectromechanical systems (MEMS). A typical MEMS-based SLM comprises a micromirror array device that further consists of an array of micromirrors mounted on movable elements. Each individual micromirror can be independently deflected by an electrostatic force. Reflection of a beam of incident light impinging a micromirror can then be controlled, for example by deflecting the micromirror through changing the electrostatic force applied to the micromirror. MEMS-based SLMs have experienced significant developments and been innovatively implemented in many applications, one of which is the use in digital display systems. In a display application, each micromirror is associated with a pixel of a displayed image. To produce a bright pixel, the state of the micromirror associated with the pixel is set in such a way that the reflected light from the micromirror is directed onto a target for viewing. To produce a dark pixel, the status of the micromirror is tuned such that the reflected light from the micromirror is directed away from the display target. In order to display a black-and-white image, the micromirror array is illuminated by a beam of light. By coordinating the reflective status of the micromirrors based on the brightness of the pixels of the desired image, the collective effect of all reflected light from individual micromirrors is the generation of the desired image. Gray-scale and colored-images can also be displayed using the micromirror array, which will not be discussed in detail.
The micromirror is a delicate device. Its performance can be significantly degraded by, for example, moistures or other particles attached to the micromirror. For this and other reasons, micromirror array devices need to be packaged after fabrication. Regardless of the differences of different packaging methods currently developed, a glass lid that is transparent to visible light is used as a window allowing incident light illuminating the micromirrors of the SLM. An air gap, however, is unavoidably formed between the glass lid and the micromirror array device. The air gap reflects incident light and thus, reduces the illumination on the micromirror array. As a consequence, the overall performance quality of the MEMS-based SLM is reduced.
Therefore, a method and an apparatus are needed for packaging micromirror array devices that reduce reflection and increase the illuminations on the micromirror devices.